AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

INTRODUCTION

Section 2 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Renal arteriovenous malformations (AVMs) are abnormal communications between the intrarenal arterial and venous systems. These malformations are either congenital or acquired (often by iatrogenic means). Renal AVMs are usually identified during the evaluation of gross hematuria. Treatment can be tailored to the individual patient. Options for therapy range from observation to embolization to nephrectomy.

Renal AVM usually refers to the congenital type of malformation. Two types of congenital renal AVMs are described. The cirsoid AVM is the most common type, and the cavernous congenital AVM is less common. On the other hand, acquired renal arteriovenous anomalies are often termed renal arteriovenous fistulas. Idiopathic renal arteriovenous fistulas have the radiographic characteristics of acquired fistulas, but no cause can be identified. They may be associated with renal artery aneurysms.

History of the Procedure

Renal AVMs were described first in 1928 by Varela. Angiographic embolization is the preferred treatment for symptomatic AVMs and has been used since the mid 1970s. Nephrectomy and partial nephrectomy are more invasive treatment options. The first planned nephrectomy was accomplished in 1869 by Simon for the treatment of ureterovaginal fistula. The first partial nephrectomy was performed for a nonmalignant renal mass by Wells in 1884.

Problem

Renal AVMs and fistulas include various abnormal connections between the intrarenal arterial and venous systems. They cause hematuria and are associated with hypertension.

Frequency

Renal AVMs are uncommon. The estimated rate in large autopsy series is less than 1 case per 30,000 patients. In clinical studies, usually including patients undergoing evaluation with urologic or vascular imaging techniques, the incidence ranges from 1 case per 1000-2500 patients.

Congenital AVMs account for less than one third of renal AVMs. Most of these are the classic cirsoid type. Congenital cirsoid AVMs have a dilated, corkscrew appearance, much like a varicose vein. Cavernous AVMs, with single dilated vessels, account for the remainder of congenital malformations.

Acquired arteriovenous fistulas are the most common and represent as many as 75-80% of renal AVMs.

Idiopathic renal arteriovenous fistula represents less than 3% of renal AVMs.

The international incidence of renal AVMs is influenced by the prevalence of percutaneous renal surgery and biopsies because these interventions cause most of the acquired renal fistulas.

Etiology

The etiology of congenital AVMs is unknown. On the other hand, the cause of acquired AVMs is usually known.

Percutaneous renal biopsy is the most common known cause of acquired renal arteriovenous fistula. An estimated 15-50% of biopsies result in some degree of fistula formation. In one study in which arteriograms were performed after every renal biopsy, radiographic evidence of fistula was identified in 15% of patients.

Trauma is another important, although uncommon, cause of acquired renal fistulas. In patients with hypertension following renal trauma, renal AVMs may occur in one third of patients. In patients with penetrating trauma, arteriovenous fistulas may affect as many as 80% of patients with posttraumatic hypertension.

Idiopathic arteriovenous fistulas are thought to arise from the spontaneous erosion or rupture of a renal artery into a nearby renal vein.

AVMs may also occur in the setting of malignancy. Renal cell carcinoma has a vascular predilection, with renal vein extension and parasitic tumor vessels both being relatively common. Angiogenic tumor factors have been implicated and may explain the development of AVMs within renal tumors.

Pathophysiology

In the cirsoid congenital AVM, multiple communications exist between the arteries and veins. These communications develop multiple coiled channels, forming a mass within the renal parenchyma. The communicating vessels are tortuous, dilated, and located beneath the lamina propria of the renal urothelium. This cluster of vascular channels forms a mass, with the arterial supply arising from one or more segmental or interlobar renal arteries. Its nearness to the collecting system may explain the high prevalence of hematuria.

The less common cavernous congenital AVM is characterized by a single artery that feeds into a single cystic chamber, with a single draining vein.

Acquired AVMs result from traumatic disruption of renal vessels. A fistulous connection between the arterial and venous systems occurs as a result of the trauma.

Any renal AVM may result in renin-mediated hypertension.

Clinical

Gross hematuria is the initial sign or symptom in most (as many as 75%) patients with a renal AVM.

Renal colic may result from obstructing blood clots, which may be voided as vermiform (wormlike) masses.

Rarely, during the evaluation of asymptomatic microscopic hematuria, an AVM is found and presumed to be the cause of hematuria.

A significant percentage of patients with renal AVMs are hypertensive. Half the patients with acquired AVMs and a quarter of the patients with congenital renal AVMs have high blood pressure. Preexisting hypertension is thought to be a risk factor for developing a fistula following a renal biopsy. Conversely, hypertension that develops following a biopsy can be due to increased renin secretion that is caused by relative hypoperfusion distal to the AVM.

Cardiomegaly, congestive heart failure (CHF), or both also may be present among patients evaluated for renal AVMs.

Rarely, a patient may present with hypotension from hemorrhage caused by an AVM. This has been described in numerous settings, including during pregnancy.

A history of a previous renal biopsy or percutaneous renal surgery is an important risk factor for the development of an acquired arteriovenous fistula. A history of renal trauma, especially a penetrating injury, is also an important risk factor for developing a renal fistula.

A physical evaluation may demonstrate findings of a flank bruit. A palpable mass is usually present in those patients with renal tumors as the cause of the fistula.

INDICATIONS

Section 3 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Gross hematuria is the primary reason for evaluation of patients with renal AVMs. The diagnostic evaluation of patients with microscopic hematuria also may lead to the discovery of an AVM. Flank pain may lead to the diagnosis of AVM, although this is unusual without the presence of hematuria. Several case reports describe the incidental discovery of AVMs on images from studies performed for other indications.

The initial means of treating renal malformation is usually arteriographically guided embolization. One indication for the treatment of renal AVMs is pain. The pain from renal AVMs results from either obstruction of the collecting system by clots or from the expansion of the renal capsule due to intrarenal hemorrhage. Persistent gross hematuria, especially in patients with anemia, may prompt treatment. Hypertension is an important indication for treatment. Attempts have been made to preoperatively determine whether the malformation is responsible for the hypertension. However, selective renal vein renin levels have not been successful in helping discriminate which patients' hypertension will respond to either embolization or nephrectomy. CHF is an unusual yet compelling indication for treatment.

Indications for surgical therapy have become more restricted as the ability to treat renal AVMs with angiographic embolization has improved. AVMs due to malignancy usually require surgical extirpation. Significant metastatic disease and poor performance status may limit the use of nephrectomy, in which embolization may be palliative. Symptomatic hematuria refractory to embolization is definitively treated by nephrectomy. In most cases, hypertension is cured by nephrectomy. Finally, pain refractory to less-invasive attempts may respond to nephrectomy.

RELEVANT ANATOMY

Section 4 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Knowledge of renal vascular anatomy is important in understanding diagnostic studies and planning therapy.

The renal artery is an end organ branch from the aorta. Supernumerary renal arteries are common (at least 25% of patients). The renal artery branches into 4 or 5 segmental renal arteries. The first branch is the posterior branch, which supplies the posterior segment of the kidney. The main artery then enters the renal hilum before dividing into the other segmental branches.

These branches of the renal artery supply minimal collateral circulation among the renal segments. The lobar renal arteries are located within the renal sinus and are branches of the segmental arteries.

The lobar arteries divide into the interlobar arteries, which are within the renal parenchyma. The interlobar arteries are in close proximity to the collecting system. The interlobar arteries divide into the arcuate arteries, which lead to the interlobular arteries.

The interlobular arteries lead to the afferent arterioles, which feed each glomerulus. Blood flows from the glomerulus to the efferent arteries, which lead to the vas recta, which, in turn, provides the network for venous drainage of the kidney.

The venous drainage follows the same pattern of branching as the arteries. However, unlike the arterial system, significant connections exist between the renal segments within the venous system.

CONTRAINDICATIONS

Section 5 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

In general, no contraindications exist for evaluating AVMs.

In a patient with allergy to contrast agents, the diagnostic evaluation may need to be altered. If iodinated contrast is used for diagnostic studies in patients with previous reactions, then medical preparation may decrease the risk of severe allergic reactions.

Severe protocols have been advocated; one regimen includes (1) administering 20-50 mg of prednisone orally 13 hours, 7 hours, and 1 hour prior to the procedure and (2) administering 50 mg of diphenhydramine orally 1 hour prior to the procedure. Additionally, histamine2-receptor antagonists are used in some centers to further decrease the risk of an allergic reaction. Also, the use of nonionic contrast is associated with a lower incidence of allergic reactions.

Alternatively, diagnostic methods that do not use iodinated contrast may be used to avoid the risk of a reaction occurring. Specifically, magnetic resonance angiography (MRA) with gadolinium and carbon dioxide angiography can provide excellent images of the renal arteries and, potentially, renal AVMs.

Impaired renal function increases the risk of using iodinated contrast in diagnostic studies, which may alter the evaluation. Diabetes, preexisting renal insufficiency, and dehydration are risk factors for contrast-induced nephropathy. The degree of renal insufficiency that precludes the use of contrast is controversial. An absolute cut-off should be avoided. The risk of nephropathy increases if the serum creatinine level is greater than 1.5 mg/dL. In some cases, the use of contrast can be justified even in patients with moderate-to-severe renal dysfunction. Nonetheless, a serum creatinine level greater than 1.5-2 mg/dL should prompt consideration of alternative diagnostic measures (eg, digital subtraction angiography, MRA, carbon dioxide angiography).

Further, hydration with intravenous isotonic sodium chloride solution, diuresis (eg, via administration of furosemide), and the administration of free-radical scavengers may decrease the frequency, duration, and severity of contrast-induced renal dysfunction. Specific free-radical scavengers include mannitol (which also facilitates diuresis) and acetylcysteine (Mucomyst). Lower doses of contrast and nonionic media are also used to diminish the risk of contrast. In most patients, renal function recovers and dialysis is rarely needed.

Gadolinium-based contrast agents (Magnevist, MultiHance, Omniscan, OptiMARK, ProHance) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic, Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or magnetic resonance angiography (MRA) scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA.

NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving or straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

Few contraindications exist to treating renal AVMs. Contrast allergy may necessitate premedication with antihistamines and steroids. Otherwise, embolization of renal AVMs is well tolerated, even among patients not able to tolerate operative intervention. However, in those patients with poor general health, especially with regard to cardiopulmonary status, surgical intervention may be contraindicated.

Additionally, renal function must be carefully assessed before nephrectomy is performed in select patients. The importance of nephron-sparing surgery is magnified in patients with underlying renal impairment. Approximately 20-25% of a single renal unit should be salvaged if possible. This provides an estimated glomerular filtration rate of 10-15%, which may keep many patients from needing dialysis for end-stage renal disease. However, ultrafiltration injury may occur when less than 25% of the total renal mass is spared.

Thus, in patients with solitary kidneys, bilateral AVMs, or renal insufficiency, detailed planning is necessary. The increased risk of partial nephrectomy is easily justified for these patients. Additionally, strong arguments can be made for the routine use of nephron-sparing approaches, especially for benign diseases such as renal AVMs, in all patients when technically feasible. This serves to protect patients from the small risk of developing renal insufficiency in the future.

WORKUP

Section 6 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Lab Studies

• In general, the laboratory evaluation is dictated by the clinical presentation of the patient.
• Hemoglobin/hematocrit
• • Anemia may contribute to the severity of heart failure in some patients with renal AVMs.
  • Further, significant hemorrhage and hemodynamic instability are associated with AVMs. In these cases, frequent assessment of the hemoglobin and hematocrit values is indicated.
• Chemistry assay
• • The assessment of renal function based on serum creatinine values is indicated before contrast-enhanced radiographic studies are performed, especially in elective scenarios and in high-risk patients (eg, patients with diabetes, those >65 y, those with known renal insufficiency).
  • Renal function also may dictate the type and timing of surgical intervention. Nephron-sparing surgery with partial nephrectomy is an important treatment option in patients with preexisting renal failure. Additionally, the diagnostic evaluation may be modified in patients with renal insufficiency. Finally, obstructive uropathy may result from gross hematuria with clots. Surgical intervention (if not emergent or needed to relieve the obstruction) should be delayed until maximal recovery of renal function is achieved.
• Coagulation parameters (ie, prothrombin time, activated partial thromboplastin time, bleeding time)
• • Coagulopathies may be responsible for bleeding that reveals the presence of an AVM.
  • Bleeding disorders should be corrected before most interventions are pursued.
• Type and crossmatch blood: The availability of crossmatched blood becomes important in hemodynamically unstable patients.
• Urinalysis/urine culture
• • Rarely, renal AVMs may be discovered during the evaluation of microscopic hematuria.
  • Urinary tract infections should be excluded before intervention is pursued.

Imaging Studies

• Choice of imaging study
• • The initial diagnostic evaluation of hematuria is debatable. No single study detects all pathologies.
  • Renal ultrasound has been advocated as an ideal initial study because renal ultrasound is noninvasive, relatively inexpensive, and helps to detect many lesions.
  • Until recently, most urologists favored the use of intravenous pyelography (IVP) for the initial evaluation of patients with hematuria.
  • CT scans are gaining favor in some centers because of the speed of the study and the detailed images of the renal parenchyma. With modern scanners and software, collecting system evaluation is also improving. Three-dimensional reconstruction with tailored studies can provide excellent anatomic detail.
  • Thus, the initial study for the evaluation of gross hematuria depends on several factors, including location, urologist and radiologist preference, and patient factors. The characteristics of renal AVMs on IVP, ultrasound, and CT scan images are described.
• Intravenous pyelography
• • The advantages include obtaining anatomic detail, especially of the collecting system, and functional information about perfusion, function, and obstruction.
  • The disadvantages include cost, radiation and contrast agent exposure, and insensitivity for small mass lesions.
  • In numerous cases, additional radiographic studies are needed, but, in most cases, IVP is a reasonable initial study for the evaluation of gross hematuria.
  • AVMs have several characteristics on IVP images. A mass lesion may be observed on the nephrotomogram images, especially in the medullary region, with compression of the collecting system. Hypoperfusion distal to the AVM may be present, which manifests as a wedge-shaped defect or segmental nonvisualization. Filling defects of the collecting system also may be present. The AVM may cause an irregular impression on the collecting system, and clots may fill and obscure a calyx or the renal pelvis. Finally, IVP results may be normal in patients with an AVM.
• Doppler ultrasound
• • Ultrasound has recently gained favor as a noninvasive means for evaluating renal causes of hematuria. The debate about the merits of ultrasound versus IVP for this purpose is beyond the scope of this article.
  • Ultrasound is more sensitive for the detection of small renal masses and can help distinguish more reliably between cystic and solid masses. However, renal ultrasound is less accurate for identifying lesions of the collecting system and provides only indirect information about renal function.
  • Doppler increases the sensitivity for vascular lesions. Several cases have been reported in which a mass lesion was correctly identified as a renal AVM by the use of color-duplex Doppler ultrasound studies. The lesions were identified as AVMs based on the turbulent blood flow within a cystic mass. Otherwise, ultrasound may not be able to help distinguish AVMs from small solid masses.
• Computed tomography
• • Further evaluation of renal lesions detected using ultrasound or IVP usually includes CT scans of the kidney. Standard abdominal scans with drip infusion of contrast may help identify an enhancing mass lesion of the kidney, often centrally located near the collecting system.
  • To differentiate such a mass from a hypervascular mass (eg, renal cell carcinoma), specific dynamic renal protocols are useful. These include noncontrast scans followed by bolus infusion of contrast. Soon after contrast administration, the patient is rescanned several times to capture the sequential stages of contrast uptake in the kidney.
  • Typical findings include early filling of the renal vein and inferior vena cava with contrast, dilation of the renal vein, and, sometimes, enlargement of the feeding renal artery. Dense contrast enhancement of the lesion during the cortical phase may be helpful, especially if the mass is located in the medulla, which typically has less early contrast enhancement.
  • With modern spiral CT scanners and bolus infusion, detailed anatomic and functional information can be obtained and can lead to the accurate diagnosis of renal AVMs.
  • CT urography has replaced IVP in some centers for the initial evaluation of hematuria. With proper equipment and oversight, CT urography, angiography, or both can provide information about renal function, as well as detailed definition of the anatomy, including the vascular and collecting systems. As such, CT angiography has replaced traditional angiography for many indications, including evaluation of the living kidney donor and preoperative planning for complex partial nephrectomy.
• Magnetic resonance angiography
• • MRI is a promising technology for the evaluation of renal masses.
  • MRA is especially useful in those patients who cannot tolerate iodine-based contrast. Several reports have confirmed the diagnostic usefulness of MRA for the diagnosis of renal AVM.

Other Tests

• Urine cytology: This is usually performed during the evaluation of hematuria, although it does not specifically contribute to the diagnosis of a renal AVM.

Diagnostic Procedures

• Angiography
• • Angiography remains the criterion standard for the clinical diagnosis of AVM. Additionally, angiography provides the means for treatment with transcatheter embolization.
  • Angiography of an AVM demonstrates rapid contrast visualization in the inferior vena cava within seconds of contrast injection because of the rapid shunting of blood from the arterial system to the venous system. Decreased density on the nephrogram also may appear distal to the AVM. The actual malformation may be a subtle blush if the AVM is small, or the multiple small tortuous vessels may be easily visualized. Cirsoid AVMs are supplied by multiple arteries, while the cavernous AVMs and arteriovenous fistulas tend to be supplied by single vessels.
• Cystoscopy
• • Because most patients with AVMs present with hematuria, cystoscopy should be performed to evaluate for coincidental lower tract pathology.
  • Cytologic evaluation of the urine is also useful for screening for carcinoma in situ of the bladder, which can be missed during diagnostic cystoscopy.

TREATMENT

Section 7 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Medical therapy

In some cases, conservative therapy can be used safely. If ablation was not performed at the time of arteriography, observation is indicated in some patients. If symptoms and hemodynamic complications do not develop, noninvasive therapy is worth a trial in those patients with small AVMs. Hematuria often improves with bedrest. Analgesics may be necessary.

Little is known about the natural history of untreated AVMs. Acquired arteriovenous fistulas tend to resolve spontaneously. A recent report describes spontaneous resolution of an AVM. Angiography findings helped confirm the radiographic disappearance of the malformation without specific intervention. Nonetheless, theoretical concerns are that expectant therapy risks delayed hemorrhage from an enlarging AVM or the development of irreversible hypertension. Because patients with AVMs usually present with symptoms, most patients receive an attempt at definitive therapy rather than mere observation.

Medical management is essential to optimizing outcome. In addition to relieving pain, hypertension should be treated. Heart failure must be controlled before surgical intervention is instituted. Blood transfusions may be needed for the rare patient with hemorrhage from an AVM. Finally, renal failure can occur as a complication of the contrast agents used during radiographic evaluation.

The initial therapy for treatment of AVMs is usually angiographically guided embolization of the malformation. Numerous substances have been injected in an effort to ablate the AVM. Initial attempts at embolization were complicated by recurrence of the AVM. This was thought to be due to the type of material used for embolization. Materials that have been used for embolization include steel coils, autologous blood clots, gelatin sponges and foams, and synthetic polymers.

The most effective material for embolization appears to be absolute alcohol, which is relatively inexpensive. Injection through the catheter lumen is also easier than with many of the synthetic materials. Balloon catheters are used to occlude the feeding artery to prevent retrograde migration of the alcohol. The alcohol denatures the proteins within the wall of the AVM, thereby inducing thrombosis and occlusion of the malformations. Superselective embolization with coils and microspheres has also been described.

Repeat treatments may be needed to completely ablate the AVM. Alcohol or other material can be used for the subsequent treatments. Epinephrine injection before embolization may make the procedure more effective by inducing vasospasm, thereby concentrating the injected material within the AVM.

Surgical therapy

The treatment most likely to cure an AVM is total nephrectomy. Total nephrectomy is indicated for large cirsoid AVMs. In most cases, nephrectomy is reserved for patients in whom more conservative therapy has failed. If the fistula is due to malignancy, then radical nephrectomy is usually indicated.

The primary criticism of nephrectomy for renal AVMs is that significant amounts of normal renal tissue are removed. Thus, reconstructive approaches have been advocated in selected circumstances. Partial nephrectomy has been accepted as a safe treatment for small, polar lesions. With increasing experience with partial nephrectomy for malignancy, partial nephrectomy will likely be attempted with greater confidence, even for large and centrally located AVMs. Additionally, to decrease the morbidity from the incisions needed for renal surgery, laparoscopic partial and total nephrectomy have been used with increasing frequency to treat selected renal AVMs.

In addition to partial nephrectomy, other techniques have been used to treat AVMs. Small malformations located in the peripheral aspect of the kidney may be treated by ligation of feeding vessels. The dissection of the feeding vessels may be technically difficult. Bench surgery with autotransplantation may facilitate the successful treatment of large and/or centrally located malformations. This degree of renal reconstruction is rarely necessary but may preserve enough functional renal tissue to avoid dialysis in select cases.

Despite being the most successful treatment for renal AVMs, surgical intervention is usually reserved for those cases refractory to embolization or those associated with malignancy.

Preoperative details

The successful treatment of renal AVMs relies on definitive localization of the lesion. Meticulous radiographic evaluation is needed because some lesions are subtle.

Medical conditions, especially CHF and hypertension, should be stabilized. Assessment of anesthetic risk is needed before open surgical intervention is pursued. Coagulopathies must be corrected before intervention. Transfusion may be needed to correct anemia.

Special attention to renal function is needed when planning operative intervention. Several circumstances exist that may impair renal function. Chronic hypertension may result in nephrosclerosis and chronic renal insufficiency. Heart failure may cause both acute and chronic renal dysfunction due to inadequate perfusion. Pharmacological therapy for either hypertension or heart failure can induce renal insufficiency. Contrast used for arteriography may cause acute renal failure, which may necessitate a delay in intervention.

Preexisting congenital anomalies, acquired abnormalities, or previous surgery may impair the function of the contralateral kidney. In these cases, global renal function should be assessed by deliberate means. Twenty-four–hour urine collection for assessment for creatinine and urea clearance may be complicated by the presence of hematuria, but it can provide an accurate assessment of renal function. Nuclear scans can help assess estimated glomerular filtration rates and split renal function. These objective data can help accurately guide the need for nephron-sparing surgery, such as partial nephrectomy.

Intraoperative details

Total or simple nephrectomy to treat renal AVMs is a routine procedure in most cases. The choice of incision and surgical approach is determined by surgeon preference, as well as by patient body habitus, AVM size, and previous incisions.

The flank extraperitoneal approach serves well for most cases, although a transabdominal approach offers early control of the main renal vessels, which may prove beneficial in some cases. The posterior approach may have less patient morbidity but is not a routine approach. Laparoscopic nephrectomy offers the patient less discomfort and an earlier return to normal activity.

The Gerota fascia may be entered or perinephric fat can be excised, usually depending on which approach is easiest at the time of surgery. Perinephric fibrosis due to subcapsular bleeding may make simple nephrectomy more difficult than excision of the perinephric fat with the kidney. The adrenal gland should be spared.

When partial nephrectomy or extracorporeal reconstruction is indicated, the kidney should usually be cooled with ice slush. Mannitol may be useful to facilitate diuresis and as a free-radical scavenger. Intraoperative ultrasound provides the means to localize small lesions.

Postoperative details

Routine postoperative care is indicated following nephrectomy, as is careful hydration and close hemodynamic monitoring. Aggressive pulmonary toilet is essential. Early ambulation is important, and activity restrictions following partial nephrectomy are becoming less stringent. Resumption of diet is influenced mostly by surgeon bias, although caution is warranted following transabdominal approaches. The influence of CHF can complicate the response to nephrectomy. In patients with AVM-induced heart failure, intensive monitoring, including pulmonary artery catheterization, may be needed.

Follow-up

Individualized follow-up care is necessary following intervention. Unless total nephrectomy is used, recurrence is possible. Additionally, hypertension and renal function should be assessed. Routine imaging is not usually indicated.

For excellent patient education resources, visit eMedicine's Kidneys and Urinary System Center. Also, see eMedicine's patient education article Blood in the Urine.

COMPLICATIONS

Section 8 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Nephrectomy complications can be classified by organ system. Cardiac complications include dysrhythmia from electrolyte imbalances caused by diuresis. Ischemia may be caused by surgical anemia or anesthetic hypotension. Pulmonary complications include atelectasis, pneumonia, pneumothorax, and pulmonary embolism. Gastrointestinal complications include ileus, pancreatitis, and duodenal injury (from retractor tension). Subcostal nerve injury and stroke are possible nervous system complications. Infections are uncommon, although Foley catheter-induced cystitis, incisional sepsis, and pneumonia are possible.

Partial nephrectomy has more potential complications. Bleeding is more common after partial nephrectomy than after total nephrectomy. Renal impairment is also reportedly more common after partial nephrectomy. This occurs most often in the setting of preexisting renal insufficiency, which may have mandated partial nephrectomy. Acute tubular necrosis can occur; renal cooling during partial nephrectomy may decrease the duration and severity of acute tubular necrosis following partial nephrectomy. However, the necessity of renal cooling during partial nephrectomy is increasingly controversial. In experienced centers, laparoscopic partial nephrectomy can be accomplished without renal surface cooling and without a significantly increased risk of acute tubular necrosis.

However, the application of laparoscopic partial nephrectomy for the treatment of renal AVM has not been well described. If the contralateral kidney is normal, renal function is usually normal postoperatively, although increased blood loss, longer duration of the operation, and reperfusion effects may rarely cause total renal impairment after partial nephrectomy.

Urinary and arteriovenous fistulas have been described after partial nephrectomy. Urinary fistulas result from an injury to the collecting system during the partial nephrectomy. Urine can drain to the skin, creating a urinary-cutaneous fistula. Most urinary fistulas and leaks can be treated successfully conservatively or with urinary drainage, often using minimally invasive techniques such as percutaneous nephrostomy and drain placement. Arteriovenous fistulas may be silent, discovered incidentally during subsequent imaging studies. They also may manifest with signs or symptoms similar to the original AVM. Thus, recurrence after partial nephrectomy is possible.

Complications after embolization include pharmacologic and technical factors. Contrast-induced nephropathy and allergic reactions may occur and can be serious. Further, the agent used for embolization may cause complications. The agent may migrate or be misdirected and thus cause damage to normal renal tissue or other organs. A recent case description noted coil and guidewire erosion into the colon. Alcohol may cause transient headaches and mild intoxication. Recurrence or persistent fistulas are possible. Hematomas and pseudoaneurysm at the puncture site (usually femoral artery) are not uncommon, with clinical evidence of hematoma occurring in approximately 5% of patients.

OUTCOME AND PROGNOSIS

Section 9 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Nephrectomy remains the criterion standard for treating renal AVMs. Hematuria due to an AVM resolves following nephrectomy, while hypertension is cured or improved in 60-85% of patients.

Further, with advances in available techniques, angiographic embolization treatment is the usual first line of therapy because it can be accomplished at the time of diagnosis, with little morbidity.

Most acquired renal fistulas resolve spontaneously.

FUTURE AND CONTROVERSIES

Section 10 of 11  

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

Renal AVMs remain an uncommon clinical problem. However, the incidence may increase as the frequency of incidental renal masses increases. Small renal masses on abdominal imaging studies performed for other symptoms are becoming more common.

Categorizing these masses as benign or malignant in an economic and safe manner has received much attention. Asymptomatic renal AVMs are a rare cause of the incidental mass, but several case reports describe clinical situations in which a renal AVM was classified incorrectly as a malignant tumor or as hydronephrosis. Specific CT scan protocols seem especially promising as a minimally invasive way to improve the classification of renal masses. Further, improvements in MRI, MRA, and Doppler ultrasound may decrease the need for the use iodinated contrast agents.

REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Indications
• Relevant Anatomy
• Contraindications
• Workup
• Treatment
• Complications
• Outcome and Prognosis
• Future and Controversies
• References

• Burkholder GV, Dotin LN, Thomason WB, Beach PD. Unexplained hematuria. How extensive should the evaluation be?. JAMA. Dec 1 1969;210(9):1729-33. [Medline].
• Cisternino SJ, Malave SR, Neiman HL. Congenital renal arteriovenous malformation: ultrasonic appearance. J Urol. Aug 1981;126(2):238-9. [Medline].
• Clouse ME, Adams DF. Congenital renal arteriovenous malformation: angiography in its diagnosis. Urology. Feb 1975;5(2):282-5. [Medline].
• Crotty KL, Orihuela E, Warren MM. Recent advances in the diagnosis and treatment of renal arteriovenous malformations and fistulas. J Urol. Nov 1993;150(5 Pt 1):1355-9. [Medline].
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Article Last Updated: Jan 5, 2007